1. Field of the Invention
The present invention relates to a micromechanical device of a micromachine such as packaging of a minute electromechanical component, and a method of manufacturing a micromechanical device.
2. Description of the Related Art
As an example of a micromechanical device shown in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-207959, and U.S. Pat. No. 7,008,812B1, a micro-electromechanical system (MEMS) 101 in which a MEMS element 104 as a micromachine having a motion is mounted on a substrate 102, and is sealed in a hollow state as shown in FIGS. 10 to 12 are known.
The MEMS 101 is constituted of a substrate 102, an insulating layer 103, a MEMS element 104, signal interconnect 105, a hollow section 106, a first sealing body 107, and a second sealing film 108. The MEMS element 104 has a cantilever or center impeller beam structure, in which the beam is formed in such a manner that a gap of several microns is held between a central part of the beam and the signal interconnect 105. In the insulating layer 103 directly under the MEMS element 104, the signal interconnect 105 is formed by using Au or the like. The MEMS element 104 is constituted of poly-Si or Al having high spring characteristics, and gets closer to the signal interconnect 105 side by being given drive force such as electrostatic force or the like. Further, when the drive force is removed, the MEMS element 104 is restored to the position in which the element 104 has a gap between itself and the signal interconnect 105 by its own spring characteristics. By changing the gap between the MEMS element 104 and the signal interconnect 105 as described above, the MEMS element 104 performs functions of variable capacitance, switching, and the like.
For the operation and protection of the MEMS element, the MEMS element needs to be sealed in a hollow state. For the purpose of reducing the manufacturing cost and the size, there is provided a method of manufacturing a micromechanical device by a film formation process. First, in order to form a gap between the micromachine and the substrate, a sacrificial layer 109 to be completely removed in the subsequent step is formed on the substrate 102. Then, a MEMS element is formed on the sacrificial layer 109. A second sacrificial layer 110 is formed on the MEMS element 104 formed on the sacrificial layer 109. An inner inorganic sealing film 107 which will become a micromechanical device is formed on the second sacrificial layer 110. Opening shape sections 107a for introducing an etching agent when the sacrificial layers 109 and 110 around the MEMS element 104 are removed during or after film formation are formed. The etching agent for removing the sacrificial layer is introduced from the opening shape sections 107a, and all the sacrificial layers 109 and 110 are completely removed. Finally, a second sealing film 108 is formed on the inner inorganic sealing film 107a until the opening shape sections 107a are completely closed.
As a result of the above, it becomes possible to seal the MEMS element 104 in a hollow state by the micro-electromechanical system 101 constituted of the first and second sealing films 107 and 108. The inside of the hollow section 106 is a reduced-pressure atmosphere.
Incidentally, here, the opening shape sections 107a are provided at a position separate from the MEMS element 104 in order that the film material may not be deposited on the MEMS element 104 because when the second sealing film 108 is formed by a film formation method such as CVD and sputtering, the film material is deposited directly under the opening shape section 107a. 
However, in the technique described above, there have been the following problems. That is, when the second sealing film 108 is formed by CVD, sputtering, or the like, and the opening shape sections 107a of the inner inorganic sealing film 107 are closed, the inside of the hollow section 106 becomes the reduced atmosphere in the thin film deposition system chamber, and the sections 107a are closed in the state where the reduced-pressure state is held. In the reduced-pressure atmosphere, the fluid resistance is small, and hence when the electrostatic force applied to the MEMS element of the spring structure is removed, vibration of the MEMS element 104 becomes difficult to be statically determinate. Thus, the vibration of the MEMS element 104 causes noise included in the output signal.
On the other hand, in order to realize reduction in size, for example, when a plurality of micromechanical devices are individually sealed, and the micromechanical devices are arranged with a small pitch, the close adhesion region becomes small. Thus, when heat is applied to the devices in the assembly process after the sealing film formation, there is the possibility of the sealing body and the substrate between the sealing films, or the sealing films being peeled off each other.
The present invention has been contrived to solve the above-mentioned problems, and an object thereof is to provide a micromechanical device of a micromachine in which noise of the output signal can be reduced by making the vibration of the micromachine easily determinate.
Another object of the present invention is to prevent the sealing films of the sealing body, or the sealing body and the substrate from being peeled off each other when heat is applied to the micromechanical device in the assembly process after the sealing film formation.